Semiconductor integrated circuit arrangement fabrication method

ABSTRACT

To realize etching with a high selection ratio and a high accuracy in fabrication of an LSI, the composition of dissociated species of a reaction gas is accurately controlled when dry-etching a thin film on a semiconductor substrate by causing an inert gas excited to a metastable state in a plasma and a flon gas to interact with each other and selectively obtaining desired dissociated species.

This is a continuation application of U.S. Ser. No. 09/188,371, filedNov. 10, 1998, now U.S. Pat. No. 5,962,347; which is a continuationapplication of U.S. Ser. No. 08/857,167, filed May 15, 1997, now U.S.Pat. No. 5,874,013; which is a File Wrapper Continuation of U.S. Ser.No. 08/472,459, filed Jun. 7, 1995, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the art of semiconductor integratedcircuit arrangement fabrication, and particularly to an art fordry-etching a thin film on a semiconductor wafer by using radicals orions in a plasma.

A silicon oxide film which is a typical insulating film used tofabricate an LSI is normally processed by a dry-etching system (plasmaetching system) using a plasma process.

In the case of an etching process using a typical magneto-microwaveplasma etching system, a vacuum chamber of the etching system comprisinga reaction chamber (etching chamber) and a discharge chamber is firstevacuated up to approx. 10⁻⁶ Torr by an evacuating system and then areaction gas is introduced into the vacuum chamber through a needlevalve to a predetermined pressure (approx. 10⁻⁵ to 10⁻¹ Torr).

The etching of a silicon oxide film deposited on a silicon wafer uses,for example, a fluorocarbon gas such as CF₄, C₂ F₆, C₃ F₈, or C₄ F₈ anda hydrogen-containing fluorocarbon gas such as CHF₃ or CH₂ F₂ or a mixedgas of a fluorocarbon-based gas and hydrogen. Hereafter, these gases aregenerally referred to as flon gases.

Microwaves of 1 to 10 GHz (ordinarily of 2.45 GHz) generated by amicrowave generator (ordinarily a magnetron) are propagated through awave guide and are introduced into a discharge tube forming a dischargechamber. The discharge tube is made of an insulating material(ordinarily quartz or alumina) in order to pass microwaves.

A magnetic field is locally formed in the discharge and reactionchambers by an electromagnet and a permanent magnet. When a microwaveelectric field is introduced into the discharge chamber under the abovestate, magnetic-field microwave discharge occurs due to a synergisticaction between the magnetic field and the microwave electric field, anda plasma is formed.

In this case, the reaction gas dissociates in the plasma and therebyvarious radicals and ions are generated. Dissociation of the reactiongas is caused because electrons in reaction gas molecules collide withthose in the plasma or absorb light, and thereby become excited toantibonding orbitals. These dissociated species are supplied to thesurface of a silicon oxide film to participate in the etching of thesilicon oxide film while dissociation species influence the dry-etchingcharacteristics in a complex way.

A dry etching system using this type of plasma process is disclosed inJapanese Patent Laid-Open No. 109728/1991.

SUMMARY OF THE INVENTION

An electronic device such as a silicon LSI or a TFT (thin-filmtransistor) has a structure in which a silicon oxide film of an objectmaterial to be dry-etched is deposited on a silicon film (e.g. siliconsubstrate, silicon epitaxial film, or polysilicon film), silicon nitridefilm, or a multilayer film made of these films.

In the case of an electronic device with a high integration level, it ispossible to open a contact hole with a diameter of 0.5 μm or less and ahigh aspect ratio (hole depth/hole diameter), and moreover etching witha high accuracy and a high selection ratio is necessary, whileminimizing the etching amount of a base silicon film, silicon nitridefilm, or a multilayer film made of these films.

To realize such an etching, it is necessary to accurately control thecomposition of dissociated species of a reaction gas. However, it isdifficult to realize this control by a conventional etching method usingdissociation of reaction gas molecules caused by collision of electronsin a plasma.

This is because selective excitation by electrons can be realized onlyon antibonding orbitals of the minimum energy, but electrons withuniform energy necessary for realizing it cannot be obtained in aplasma. Therefore, it is necessary to produce electrons with uniformenergy outside and introduce them into the plasma or introduce a lightsource with a uniform energy into the plasma. In this case, however, thecost of the etching system greatly increases.

It is an object of the present invention to provide a technique ofrealizing etching with a high selection ratio and a high accuracy.

The above and other objects and novel features of the present inventionwill become apparent from the description of this specification andaccompanying drawings.

The outline of representatives embodiments of the inventions disclosedin this application will be briefly described below.

(1) In a semiconductor integrated circuit arrangement fabrication methodof the present invention, desired dissociated species are produced byallowing an inert gas excited to a metastable state in a plasma and areaction gas necessary for dry-etching a thin film on a semiconductorsubstrate to interact with each other when dry-etching the thin film.

(2) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (1), the dissociationof the reaction gas caused by collision with electrons is reduced byseparating a plasma generation chamber of a plasma dry-etching systemfrom the reaction chamber, and preventing electrons in the plasma fromentering the reaction chamber.

(3) In a semiconductor integrated circuit arrangement fabrication methodof the present invention, desired dissociated species are selectivelyproduced by allowing an inert gas excited to a metastable state in aplasma and a flon gas to interact with each other when dry-etching asilicon oxide film on a semiconductor substrate.

(4) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3), the flon gas is achain perfluorocarbon with two or more carbon atoms.

(5) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3), the flon gas is achain perfluorocarbon with two to six carbon atoms.

(6) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3), the flon gas is acyclic perfluorocarbon with three or more carbon atoms.

(7) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3) the inert gas isone or more rare gases selected out of the group of He, Ne, Ar, Kr, andXe.

(8) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3), dissociatedspecies with a high selection ratio to silicon nitride are produced.

(9) In a semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (3), the proportion ofthe inert gas to the total gas flow rate is 50% or more and theprocessing pressure is 100 mTorr to 1 Torr.

(10) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (3), theproportion of the inert gas to the total gas flow rate is 80% or moreand the processing pressure is 100 to 500 mTorr.

(11) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (3), aninorganic material is used as a mask for dry etching.

(12) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention, desired dissociated species areselectively produced by allowing an inert gas excited to a metastablestate in a plasma and a flon gas to interact with each other when asilicon nitride film on a semiconductor substrate is dry-etched.

(13) In the semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (12),dissociated species with a high selection ratio to silicon are producedby using one or more rare gases selected out of the group of He, Ar, Kr,and Xe as the inert gas and difluoromethane as the flon gas.

(14) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (3), theproportion of the inert gas of the total gas flow rate is 80% or moreand the processing pressure is 100 to 500 mTorr.

(15) A semiconductor integrated circuit arrangement fabrication methodof the present invention comprises the following steps (a) to (d):

(a) forming a field insulating film with a LOCOS structure on a mainsurface of a semiconductor substrate and thereafter forming asemiconductor element in an active region enclosed by the fieldinsulating film,

(b) depositing a first insulating film on the whole surface of thesemiconductor substrate and thereafter depositing a second insulatingfilm at an etching rate different from that of the first insulating filmon the first insulating film,

(c) selectively producing dissociated species for maximizing theselection ratio of the second insulating film to the first insulatingfilm by allowing an inert gas excited to a metastable state in a plasmaand a flon gas to interact with each other and etching the secondinsulating film by using the dissociated species, and

(d) selectively producing dissociated species for maximizing theselection ratio of the first insulating film to the semiconductorsubstrate by allowing an inert gas excited to a metastable state in aplasma and a flon gas to interact with each other, and making a contacthole connected to the semiconductor substrate and locally overlappedwith the field insulating film by etching the first insulating film withthe dissociated species.

(16) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (15), the secondinsulating film is etched by using an inorganic material deposited onthe second insulating film as a mask.

(17) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (15), thediameter of the contact hole is 0.3 μm or less.

(18) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (16), the maskmade of the inorganic material is formed from the same material as thatof the first insulating film.

(19) A semiconductor integrated circuit arrangement fabrication methodof the present invention comprises the following steps (a) to (d):

(a) forming a MISFET on a main surface of a semiconductor substrate,

(b) depositing a first insulating film on the whole surface of thesemiconductor substrate and thereafter depositing a second insulatingfilm at an etching rate different from that of the first insulating filmon the first insulating film,

(c) selectively producing dissociated species for maximizing theselection ratio of the second insulating film to the first insulatingfilm by allowing an inert gas excited to a metastable state in a plasmaand a flon gas to interact with each other and etching the secondinsulating film by using the dissociated species, and

(d) selectively producing dissociated species for maximizing theselection ratio of the first insulating film to the semiconductorsubstrate by allowing an inert gas excited to a metastable state in aplasma and a flon gas to interact with each other, and making a contacthole connected to the semiconductor substrate between the gate electrodeof the MISFET and that of a MISFET adjacent to the former MISFET andlocally overlapped with the gate electrodes by etching the firstinsulating film with the dissociated species.

(20) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (19), the secondinsulating film is etched by using an inorganic material formed on thesecond insulating film as a mask.

(21) In a semiconductor integrated circuit arrangement fabricationmethod of the present invention according to the method (19), thediameter of the contact hole is 0.25 μm or less.

(22) In semiconductor integrated circuit arrangement fabrication methodof the present invention according to the method (20), the mask made ofthe inorganic material is formed from the same material as that of thefirst insulating film.

An inert gas is excited to a metastable state whose transition to theground state is inhibited by the interaction with a plasma. Because thespontaneous emission life under the metastable state (average time inwhich the metastable state naturally changes to the ground state) is onthe order of one second, a lot of metastable-state inert gas can bepresent in a reaction chamber. The metastable-state inert gas releasesenergy due to collision and changes to the ground state. The releasedenergy is uniform and therefore makes it possible to selectively excitereaction gas molecules.

The following is the description of actions of a rare gas which is atypical example of an inert gas. Table 1 shows the metastable levelenergies of rare gases (He, Ne, Ar, Kr, and Xe) (Note 1).

                  TABLE 1                                                         ______________________________________                                        Metastable level energies of rare gases                                       Rare gas element                                                                             Metastable level energy (eV)                                   ______________________________________                                        He             19.82     20.61                                                Ne             16.62     16.72                                                Ar             11.55     11.72                                                Kr              9.92     10.56                                                Xe              8.32      9.45                                                ______________________________________                                         Note 1: J. S. Chang, R. M. Hobson, Yukimi Ichikawa, Teruo Kaneda,             "DENRIKITAI NO GENSHI BUNSHI KATEI" p. 142 (TOKYO DENKI DAIGAKU SHUPPAN       KYOKU, 1982).                                                            

As shown in Table 1, every rare gas is limited in the types ofmetastable states which can be used. Therefore, it is necessary that theantibonding orbitals of flon gas molecules to be introduced are presentat places coinciding with the metastable level energy of a rare gas, anddissociated species from the antibonding orbital must be preferable toetching.

Moreover, it is necessary to know the adhesive property, etchingproperty, and selectivity as the properties of dissociated species usedfor etching a silicon oxide film. Table 2 shows dissociated speciesbelonging to respective properties.

                  TABLE 2                                                         ______________________________________                                        Properties and examples of dissociated species                                Property      Dissociated species                                             ______________________________________                                        Adhesive property                                                                           CF.sub.2, C.sub.2 F.sub.4, CH.sub.2, CHF, CF, CH                Etching property                                                                            CF.sub.2, C.sub.2 F.sub.4, CF.sub.3, F, CHF.sub.2, CF,                        CHF, CF.sub.2+, C.sub.2 F.sub.4+, CF.sub.3+, F.sub.+,                         CHF.sub.2+,                                                                   CF.sub.+, CHF.sub.+                                             Selectivity (To Si)                                                                         CH.sub.2, C.sub.2 F.sub.4, CHF.sub.2, CF, CHF, CF.sub.2+,                     C.sub.2 F.sub.4+, CHF.sub.2+, CF.sub.+, CHF.sub.+               Non-selectivity                                                                             CF.sub.3, F, CF.sub.3+, F.sub.+                                 Non-etching property                                                                        CH.sub.2, HF, CH                                                Bombardment vertical                                                                        CF.sub.2+, C.sub.2 F.sub.4+, CF.sub.3+, F.sub.+,                              CHF.sub.2+, CF.sub.+,                                           to substrate  CHF.sub.+, CH.sub.2+, CH.sub.+                                  Bombardment   CF.sub.2, C.sub.2 F.sub.4, CF.sub.3, F, CHF.sub.2, CF,          isotropic to  CHF, CH.sub.2, CH                                               substrate                                                                     ______________________________________                                    

To improve the selection ratio, it is necessary to remove non-selectivedissociated species. Moreover, to keep the etching shape accuracy, it isnecessary to use dissociated species having a selectivity and anadhesive property. From the properties in Table 2, it will be understoodthat the dissociated species in the row of non-selectivity arepreferable. The etching rate can be obtained by ordinary system controlsuch as controlling the introduced amount of reaction gases, mixingratio of the reaction gases, and the power.

Dissociation from an antibonding orbital can be known by molecularorbital calculation (Note 2). The calculation accuracy can be evaluatedby calculating the metastable state of a rare gas and the knownreactions of molecules. Table 3 shows measurement results (Note 3) andcalculation results of reactions of monosilane (SiH₄).

                  TABLE 3                                                         ______________________________________                                        Calculation result of resonance dissociation of SiH.sub.4                                                        Dissociated                                     Measured  Calculated          species                                         metastable                                                                              excitation Calculated                                                                             (Coincides                                      level     energy of  transition                                                                             with measure-                              Gas  energy    molecule   route    ment result.)                              ______________________________________                                        He   21.2 eV   21.2 eV    None     SiHx.sub.+                                                (Semi-              Si*                                                       bonding                                                                       orbital)                                                       Ar   11.7 eV   12.2 eV    Transition                                                                             SiHx                                                      (Non-      from 8.6-                                                                              SiH*                                                      antibonding                                                                              to 8.8-eV                                                                              Si*                                                       orbital)   antibonding                                                                   orbital                                             ______________________________________                                    

Note 2: K. Kobayashi, N. Kurita, H. Kumahora, and K. Tago, Phs. Rev.B45, 11299 (1992); K. Kobayashi, N. Kurita, H. Kumahora, and K. Tago,Phys. Rev. A43, 5810 (1991); K. Tago, H. Kumahora, N. Sadaoka, and K.Kobayashi, Int. J. S. Supercomp. Appl. 2, (1988) 58.

Note 3: M. Tsuji, K. Kobayashi, S. Yamaguchi, and Y. Nishimura, Che.Phys. Lett. 158, 470 (1989).

From Table 3, it will be understood that the energy of the antibondingorbital of a molecule can be measured at an accuracy of within 1 eV bymolecular orbital calculation.

Moreover, by the molecular-orbit calculation, it is possible to knowmolecules to be selected to produce dissociated species shown in the boxof "Selectivity" in Table 2. From the calculation for dissociatedspecies and molecules for producing the species shown in Table 3, itwill be understood that the energy necessary for neutral dissociation is2 eV or more, the minimum energy necessary for excitation to theantibonding orbital is 5 to 12 eV, and the ionization potential of adissociated species is 10 to 13 eV.

From the above facts, it will be further understood that the energynecessary for ionic dissociation is 12 eV or more. Therefore, selectiveproduction of ionic and neutral dissociated species can be expected fromHe and Ne and selective neutral dissociation of Ar, Kr, and Xe can beexpected.

Moreover, by examining the dissociation from the antibonding orbitalthrough the molecular orbital calculation, it is possible to examinewhether or not an antibonding orbital from which the selectivedissociated species are produced in Table 2 is present in each molecule.Table 4 shows molecules in which the antibonding orbital is present andits excitation energy is close to the metastable level energy of a raregas. Examined molecules are CF₄, CHF₃, C₂ F₄ and C₄ F₈, of the out offlon gases.

                  TABLE 4                                                         ______________________________________                                        Flon gas molecule having antibonding                                          orbital from which selective dissociation                                     species are produced                                                                         Molecule having                                                                              Molecule having                                      Selective antibonding orbital                                                                          antibonding orbital                                  dissocia- from which non-selective                                                                     from which non-selective                        Rare tion      dissociation species                                                                         dissociation species                            gas  species   are not produced                                                                             are produced                                    ______________________________________                                        He   CH.sub.2+ C.sub.2 F.sub.4, CH.sub.2 F.sub.2                                   C.sub.2 F.sub.4+                                                                        C.sub.4 F.sub.8                                                     CHF.sub.2+                                                                              CH.sub.2 F.sub.2                                                    CF.sub.2  C.sub.2 F.sub.4                                                     C.sub.2 F.sub.4                                                                         C.sub.4 F.sub.8                                                Ne   CF.sub.2+ C.sub.2 F.sub.4                                                                              C.sub.4 F.sub.8 (Transition from                     C.sub.2 F.sub.4+         non-antibonding                                      CHF.sub.2+                                                                              CH.sub.2 F.sub.2                                                                             orbital)                                             CF.sub.2  C.sub.2 F.sub.4, CH.sub.2 F.sub.2                                                            CHF.sub.3                                            C.sub.2 F.sub.4          C.sub.4 H.sub.8                                      CHF                      (Same as the above)                                                           C.sub.4 F.sub.8                                                               (Same as the above)                                                           CHF.sub.3                                       Ar   CF.sub.2  C.sub.2 F.sub.4, C.sub.4 F.sub.8                                                             CHF.sub.3, CF.sub.4                                  CHF.sub.2                CHF.sub.3                                            CHF                      CHF.sub.3                                       Kr   CF.sub.2  CH.sub.2 F.sub.2                                                                             CF.sub.4                                             C.sub.2 F.sub.4                                                                         C.sub.4 F.sub.8                                                     CHF.sub.2 CH.sub.2 F.sub.2                                                                             CH.sub.3                                             CHF       CH.sub.2 F.sub.2                                               Xe   CF.sub.2  CH.sub.2 F.sub.2                                                                             CH.sub.2 F.sub.2                                     C.sub.2 F.sub.4                                                                         C.sub.4 F.sub.8                                                ______________________________________                                    

When using selective dissociation due to interaction with ametastable-state rare gas, dissociation due to electrons in a plasma isalso slightly present. Moreover, in the case of an actual etchingprocess, there is a possibility that non-selective dissociation speciesare expelled due to ion incidence. Therefore, it may be necessary to mixadhesive CHF or CF with a small etching rate in order to protect a sidewall. In this case, it is necessary to use the selective dissociationfrom CH₂ F₂.

Moreover, when using the protective dissociation species together,preferable etching is also realized by using the selective dissociationof CHF₃ from which production of non-selective dissociation species isrelatively small. However, because CF₄ produces a lot of non-selectivedissociation species, it is necessary to increase the amount ofprotective gas when combining CHF₃ with CF₄.

Furthermore, even if the etching method of the present invention usingselective dissociation is combined with a conventional etching methodnot using the selective dissociation due to interaction with ametastable-state rare gas or an etching method using selectivedissociation by which a lot of non-selective dissociation species areproduced, a preferable result is obtained because it is possible tocontrol the ratio of dissociation species by the mixing ratio.

When using the selective dissociation due to interaction with ametastable-state rare gas by controlling the dissociation by electronsin a plasma, it is necessary to spatially separate a rare-gas plasmachamber from an introduced-gas dissociation reaction chamber. Because itis possible to introduce positive ions and an electrically-neutralmetastable-state rare gas into the dissociation reaction chamber bypartitioning the two chambers by a grid, selective dissociation and ionassisted etching are realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a microwave plasma etching system used inEmbodiment 1 of the present invention

FIGS. 2-6 are sectional views of an essential portion of a semiconductorsubstrate, showing Embodiment 1 of a semiconductor integrated circuitarrangement fabrication method of the present invention;

FIG. 7 is a schematic view of a plasma etching system used in Embodiment2 of the present invention;

FIGS. 8-12 are sectional views of an essential portion of asemiconductor substrate, showing Embodiment 2 of a semiconductorintegrated circuit arrangement fabrication method of the presentinvention;

FIG. 13 is a schematic view of a microwave plasma etching system used inEmbodiment 3 of the present invention;

FIGS. 14-18 are sectional views of an essential portion of asemiconductor substrate, showing Embodiment 3 of the semiconductorintegrated circuit arrangement fabrication method of the presentinvention; and

FIGS. 19-23 are sectional views of an essential portion of thesemiconductor substrate, showing Embodiment 4 of a semiconductorintegrated circuit arrangement fabrication method of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will BE described below in detailreferring to the accompanying drawings.

[Embodiment 1]

FIG. 1 is a schematic view of a microwave plasma etching system 100 usedin this embodiment. The system 100 includes a microwave guide 101,magnets 102a and 102b, a plasma generation change 103, and a a reactionchamber 106. Microwaves of 2.45 GHz generated by a magnetron areintroduced into the plasma generation chamber 103 through the microwaveguide 101. Moreover, a material gas G is introduced into the plasmageneration chamber 103 through a gas introduction port 104.

By introducing microwaves into the plasma generation chamber 103 andgenerating a magnetic field of approx. 1 KG by the magnets 102a and102b, the material gas G is transformed into a plasma by electroncyclotron resonance at an ECR position 105 with a flux density ofapprox. 875 G.

In this case, neutral dissociated species and ionic dissociated speciesgenerated from the material gas G are transferred to the surface of asemiconductor substrate (wafer) 1 in the reaction chamber 106. Asusceptor 107 for supporting the semiconductor substrate 1 is connectedto a radio-frequency power supply 108 which applies a radio frequency tothe semiconductor substrate 1 to generate a self-bias and control theion energy.

The following is the description of the etching process of thisembodiment using the microwave plasma etching system 100. This is aprocess widely used as an element isolation technique for making aconnection hole in an insulating film in order to make contact with asilicon substrate adjacent to a field insulating film of a LOCOS (LocalOxidation of Silicon) structure.

Conventionally, it has been necessary to make such a connection hole sothat it does not overlap with a field insulating film. This is becausethe substrate is exposed and the element isolation property of the fieldinsulating film is deteriorated if the base field insulating film isremoved due to overetching when making the connection hole bydry-etching the insulating film.

In the case of a layout design that does not allow the overlap betweenthe connection hole and the insulating film, it is difficult to realizean LSI with a design rule of approx. 0.3 μm or less because ofrestrictions by the mask alignment accuracy of the photolithographyprocess or the like.

Therefore, in the case of this embodiment, as shown in FIG. 2, a fieldinsulating film 2 of the LOCOS structure is formed on a main surface ofthe single-crystalline silicon semiconductor substrate 1, and then asemiconductor device such as a MISFET is formed in an active regionenclosed by the field insulating film 2 by an ordinary method.

The MISFET comprises a gate electrode 3 made of a polysilicon film, agate insulating film 4 made of a silicon oxide film, and a pair ofsemiconductor regions (source region and drain region) 5, 6 formed onthe semiconductor substrate 1. Moreover, the top and side walls of thegate electrode 3 are protected by a silicon oxide film 7.

Then, a silicon nitride film 8 with a thickness of 500 to 2,000 Å isdeposited on the whole surface of the semiconductor substrate 1 by a CVDprocess and moreover, a BPSG (Boro Phospho Silicate Glass) film 9 with athickness of 5,000 to 10,000 Å is deposited on the film 8 by a CVDprocess.

Then, as shown in FIG. 3, a photoresist pattern 10 is formed on the BPSGfilm 9. The photoresist pattern 10 has an opening 11 above the onesemiconductor region 5 of the MISFET. The opening 11 is so made that oneend of the opening 11 overlaps with the field insulating film 2 adjacentto the semiconductor region 5.

Then, the semiconductor substrate 1 is loaded into the reaction chamber106 of the microwave plasma etching system 100 to dry-etch the BPSG film9 by using the photoresist pattern 10 as a mask. This etching is soperformed that the selection ratio of the BPSG film 9 to the basesilicon nitride film 8 is maximized. That is, the material gas G is madeof a mixture gas of a flon reaction gas and an inert gas shown in Table5, and the proportion of the inert gas is set to 80% or more of thetotal amount of the mixture gas. Moreover, in this case, the processingpressure is set to 100 to 500 mTorr.

                  TABLE 5                                                         ______________________________________                                        Conditions of etching BPSG layer and                                          increasing selection ratio to Si.sub.3 N.sub.4                                Reaction gas                                                                  (Flon gas)    Inert gas                                                       ______________________________________                                        C.sub.4 F.sub.8                                                                             He, Ar, Kr, Xe                                                  C.sub.2 F.sub.4                                                                             He, Ne, Ar                                                      ______________________________________                                    

FIG. 4 shows a state that the etching of the BPSG film progresseshalfway and the silicon nitride film 8 on the field insulating film 2 isexposed from the bottom of the opening 11.

FIG. 5 shows a state that the etching of the BPSG film 9 ends. In thecase of this embodiment, because the BPSG film 9 is etched under thecondition that the selection ratio to the silicon nitride film 8 ismaximized, the silicon nitride film 8 serves as a stopper of etching andit is possible to prevent the field insulating film 2 from being removedeven if adequate overetching is performed.

FIG. 6 shows a state that a connection hole 12 reaching thesemiconductor region 5 of the MISFET is completed by removing theresidual silicon nitride film 8 through etching.

The silicon nitride film 8 is etched by the microwave plasma etchingsystem 100 under the condition that the selection ratio of the siliconnitride film 8 to the base semiconductor substrate 1 is maximized. Thatis, the material gas G is made of a mixture gas of a flon reaction gasand an inert gas shown in Table 6, and the proportion of the inert gasis set to 80% or more of the total amount of the mixture gas. Moreover,in this case, the processing pressure is set to 100 to 500 mTorr.

                  TABLE 6                                                         ______________________________________                                        Conditions of etching Si.sub.3 N.sub.4 layer and                              increasing selection ratio to Si                                              Reaction gas                                                                  (Flon gas)    Inert gas                                                       ______________________________________                                        CH.sub.2 F.sub.2                                                                            He, Ar, Kr, Xe                                                  ______________________________________                                    

Therefore, this embodiment makes it possible to make the connection hole12 locally overlapping with the field insulating film 2 without removingthe field insulating film 2, and thereby realize an LSI with a designrule of 0.3 μm or less.

[Embodiment 2]

FIG. 7 is a schematic view of a plasma etching system 200 used in thisembodiment. The plasma etching system 200 is provided with an antenna202 around a quartz cylinder 201 so as to introduce electromagneticwaves into the cylinder 201 by applying a radio frequency to the antenna202. Double coils 204 and 205 are provided to the outside of a vacuumchamber 203 so as to generate a magnetic field in the axial direction. Amaterial gas G introduced through a gas introduction port 206 istransformed into a plasma by the axis-directional magnetic field and theradio frequency, and neutral dissociated species and ionic speciesgenerated during this time are transferred to the surface of thesemiconductor substrate 1 where etching is performed.

Embodiment 1 uses the photoresist pattern 10 as a mask for etching theBPSG film 9. In this case, however, the products produced whenphotoresist is etched have an influence on the selectivity that must beconsidered. That is, it is necessary to determine the photoresistmaterial and the etching condition which prevent the products producedby the etching from producing non-selective species.

Therefore, in this embodiment, a silicon nitride film 13 with athickness of 500 to 2,000 Å is deposited on a BPSG film 9 by a CVDprocess before forming a photoresist pattern 10 on the silicon nitridefilm 13 as shown in FIG. 8. The photoresist pattern 10 has an opening 11above one semiconductor region 5 of a MISFET, such that one end of theopening 11 overlaps with a field insulating film 2 adjacent to thesemiconductor region 5.

Then, as shown in FIG. 9, the silicon nitride film 13 is etched under ageneral etching condition by using the photoresist pattern 10 as a mask.

Then, the photoresist pattern 10 is removed by ashing and thereafter theBPSG film 9 is dry-etched by using the silicon nitride film 13 as amask. This etching is performed under a condition that the selectionratio of the BPSG film 9 to the silicon nitride film 13 (and the siliconnitride film 8) is maximized. That is, the etching is performed by usinga mixture gas of a flon reaction gas and an inert gas shown in Table 7,setting the content of the inert gas to 80% or more of the total amountof the mixture gas, and setting the processing pressure to 100 to 500mTorr.

                  TABLE 7                                                         ______________________________________                                        Conditions of etching BPSG layer and                                          increasing selection ratio to Si.sub.3 N.sub.4                                Reaction gas  Inert gas                                                       ______________________________________                                        C.sub.4 F.sub.8                                                                             He, Ar, Kr, Xe                                                  C.sub.2 F.sub.4                                                                             He, Ne, Ar                                                      ______________________________________                                    

FIG. 10 shows a state that the etching of the BPSG film 9 progresseshalfway and the silicon nitride film 8 on the field insulating film 2 isexposed from the bottom of the opening 11.

FIG. 11 shows a state that the etching of the BPSG film 9 ends. Becausethe BPSG film 9 is etched under the condition that the selection ratioto the silicon nitride film 8 is maximized, the silicon nitride film 8serves as a stopper of the etching, and it is possible to prevent thefield insulating film 2 from being removed even if sufficientoveretching is performed.

FIG. 12 shows a state that a connection hole 12 reaching thesemiconductor region 5 of the MISFET is completed by removing theresidual silicon nitride films 8 and 13 through etching.

The silicon nitride films 8 and 13 are etched under the condition thatthe selection ratio of the silicon nitride films 8 and 13 to the basesemiconductor substrate 1 is maximized by using the plasma etchingsystem 200. That is, the material gas G is made of a mixture gas of aflon reaction gas and an inert gas shown in Table 8 and the proportionof the inert gas is set to 80% or more of the total amount of themixture gas. Moreover, in this case, the processing pressure is set to100 to 500 mtorr.

                  TABLE 8                                                         ______________________________________                                        Conditions of etching Si.sub.3 N.sub.4 layer and                              increasing selection ratio to Si                                              Reaction gas  Inert gas                                                       ______________________________________                                        CH.sub.2 F.sub.2                                                                            He, Ar, Kr, Xe                                                  ______________________________________                                    

Therefore, in this embodiment using no photoresist for the mask foretching the BPSG film 9, the influence on selectivity due to theproducts produced when the photoresist is etched is eliminated, andthereby the etching selectivity is further improved.

[Embodiment 3]

FIG. 13 is a schematic view of a microwave plasma etching system 300used in this embodiment. The system 300 includes a microwave guide 301,a magnet 302, and a plasma generation chamber 303. Microwaves of 24.5GHz generated by a magnetron are introduced into the plasma generationchamber 303 through the microwave guide 301.

A plasma of an inert gas introduced through a gas introduction port 304is generated in the plasma generation chamber 303.

A plurality of grid electrodes 306 are provided along the boundarybetween the plasma generation chamber 303 and a reaction chamber 305 andonly ions (i.e., not electrons) the plasma are introduced into thereaction chamber 305 by alternately changing the potentials of the gridelectrodes 306 to positive and negative states. Metastable atoms of theinert gas is introduced into the reaction chamber 305 while diffusingisotropically because they are not influenced by an electric field.

A reaction gas is introduced into the reaction chamber 305 through a gasintroduction port 307 and predetermined dissociated species aregenerated due to the interaction with the metastable atoms of the inertgas. Then, the dissociated species and the ions of the inert gas aretransferred to the surface of the semiconductor substrate 1, and etchingstarts and progresses.

An etching process using the microwave plasma etching system will bedescribed below. This is a processing of making a connection hole in aninsulating film in order to make contact with a silicon substratebetween two adjacent MISFET gate electrodes.

For example, though the space between gate electrodes is decreased up toapprox. 0.25 μm, it is impossible to make a connection hole between thegate electrodes when the resolution of a photomask used to make theconnection hole is approx. 0.3 μm.

Therefore, in this embodiment, a field insulating film 2 is formed on amain surface of a semiconductor substrate 1 and then a MISFET comprisinga gate electrode 3, a gate insulating film 4, and a pair ofsemiconductor regions (source region and drain region) 5 and 6 areformed in an active region enclosed by the field insulating film 2 by anordinary method as shown in FIG. 14. In this case, the space betweenadjacent gate electrodes 3 is approx. 0.25 μm. Moreover, the top andside wall of the gate electrodes 3 are protected by a silicon oxide film7.

Then, a silicon nitride film 15 with a thickness of 500 to 2,000 Å isdeposited on the whole surface of the semiconductor substrate 1 by a CVDprocess and moreover, a BPSG film 16 with a thickness of 5,000 to 10,000Å is deposited on the film 15 by a CVD process.

Then, as shown in FIG. 15, a photoresist pattern 17 is formed on theBPSG film 16. The photoresist pattern 17 has an opening 18 above onesemiconductor region 6 of the MISFET. The opening 18 has a diameter ofapprox. 0.3 μm which is larger than the space (approx. 0.25 μm) betweenthe gate electrodes 3. That is, the opening 18 is so provided that partof the opening 18 overlaps with the gate electrodes 3.

Then, the semiconductor substrate 1 is loaded into the reaction chamber305 of the microwave plasma etching system 300 to dry-etch the BPSG film16 by using the photoresist pattern 17 as a mask. This etching is soperformed that the selection ratio of a BPSG film 16 to the base siliconnitride film 15 is maximized.

That is, the material gas G is made of a mixture gas of a flon reactiongas with an inert gas shown in Table 7, and the proportion of the inertgas is set to 80% or more of the total amount of the mixed gas.Moreover, in this case, the processing pressure is set to 100 to 500mTorr.

FIG. 16 shows a state that the etching of the BPSG film progresseshalfway and the silicon nitride film 15 is exposed from the bottom ofthe opening 18.

FIG. 17 shows a state that the etching of the BPSG film 16 ends. In thisembodiment, because the BPSG film 16 is etched under the condition thatthe selection ratio to the silicon nitride film 15 is maximized, thesilicon nitride film 15 serves as a stopper of the etching andresultingly, it is possible to prevent the silicon oxide film 7 forprotecting the gate electrodes 3 from being removed even if sufficientoveretching is performed.

FIG. 18 shows a state that a connection hole 19 reaching thesemiconductor region 6 of the MISFET is completed by removing theresidual silicon nitride film 15 through etching. The silicon nitridefilm 15 is etched by the microwave plasma etching system 300 under thecondition that the selection ratio of the silicon nitride film 15 to thebase semiconductor substrate 1 is maximized. That is, the material gas Gis made of a mixture gas of a flon reaction gas and an inert gas shownin Table 8, and the proportion of the inert gas is set to 80% or more ofthe total amount of the mixture gas. Moreover, in this case, theprocessing pressure is set to 100 to 500 mTorr.

As described above, by this embodiment, it is possible to realize an LSIwith a space between the gate electrodes 3 of approx. 0.25 μm because itis possible to make the connection hole 19 overlapped with the gateelectrodes 3 without removing the silicon oxide film 7 protecting thegate electrodes 3.

[Embodiment 4]

The above embodiment 3 uses the photoresist pattern 17 as a mask foretching the BPSG film 16. In this embodiment, however, it is necessaryto select a photoresist material and etching conditions so as to preventthe products produced when photoresist is etched from producingnon-selective dissociated species.

Therefore, in this embodiment, a silicon nitride film 20 with athickness of 500 to 2,000 Å is deposited on a BPSG film 16 by a CVDprocess to form a photoresist pattern 17 on the silicon nitride film 20as shown in FIG. 19.

Then, as shown in FIG. 20, the silicon nitride film 20 is etched underordinary etching conditions by using the photoresist pattern 17 as amask.

Then, the photoresist pattern 17 is removed by ashing and thereafter theBPSG film 16 is dry-etched by using the silicon nitride film 20 as amask. This etching is performed under the condition that the selectionratio of the BPSG film 16 to the silicon nitride film 20 (and thesilicon nitride film 15) is maximized by using the microwave plasmaetching system 300. That is, the etching is performed by using a mixturegas of a flon reaction gas and an inert gas shown in Table 7, andsetting the proportion of the inert gas to 80% or more of the totalamount of the mixture gas and the treatment pressure to 100 to 500mTorr.

FIG. 21 shows a state that the etching of the BPSG film 16 progresseshalfway and the silicon nitride film 15 is exposed from the bottom ofthe opening 18.

FIG. 22 shows a state that the etching of the BPSG film 16 ends. Becausethe BPSG film 16 is etched under the condition that the selection ratioto the silicon nitride film 15 is maximized, the silicon nitride film 15serves as a stopper of the etching, and it is possible to prevent thesilicon oxide film 7 for protecting the gate electrodes 3 from beingremoved even if sufficient overetching is performed.

FIG. 23 shows a state that a connection hole 19 reaching thesemiconductor region 6 of the MISFET is completed by removing theresidual silicon nitride films 15 and 20 through etching. The siliconnitride film 15 is etched under the condition that the selection ratioof the silicon nitride film 15 to the base semiconductor substrate 1 ismaximized by using the plasma etching system 300. That is, the materialgas G is made of a mixture gas of a flon reaction gas and an inert gasshown in Table 8, and the proportion of the inert gas is set to 80% ormore of the total amount of the mixture gas. Moreover, in this case, theprocessing pressure is set to 100 to 500 mTorr.

Thus, by this embodiment using no photoresist for the mask for etchingthe BPSG film 16, the influences of selectivity due to the productsproduced when the photoresist is etched are eliminated, and thereby theetching selectivity is further improved.

The present invention has been concretely described above by way of itspreferred embodiment. However, the present invention is not restrictedto embodiments, but various modifications of the present invention canbe realized as long as they do not deviate from the gist of the presentinvention.

The reactive gases and inert gases used in the invention are not limitedto the combinations of Embodiments 1 to 4. It should be noted that, forexample, the combinations shown in Table 9 can be adopted.

                  TABLE 9                                                         ______________________________________                                        Classification of combinations of inert gases                                 and reaction gas species according to                                         properties of selective dissociated species                                                            Production of                                        Production of                                                                              Production of                                                                             selective and non-                                   only selective                                                                             selective and                                                                             selective dissociated species                        Rare  dissociated                                                                              protective disso-                                                                         Small   Large                                    gas   species    ciated species                                                                            quantity                                                                              quantity                                 ______________________________________                                        He    C.sub.2 F.sub.4, C.sub.4 F.sub.8                                                         CH.sub.2 F.sub.2                                             Ne    C.sub.2 F.sub.4                                                                          CH.sub.2 F.sub.2                                                                          C.sub.4 F.sub.8,                                                              CHF.sub.3                                        Ar    C.sub.2 F.sub.4, C.sub.4 F.sub.8                                                                     CHF.sub.3                                                                             CF.sub.4                                 Kr    C.sub.4 F.sub.8                                                                          CH.sub.2 F.sub.2                                                                          CHF.sub.3                                                                             CF.sub.4                                 Xe    C.sub.4 F.sub.8                                                                          CH.sub.2 F.sub.2                                             ______________________________________                                    

The combinations of the reaction gases and the inert gases shown in theabove Table 9 are grouped into the following:

A: Set of combinations of inert gases and reaction gas species producingonly selective dissociated species;

B: Set of combinations of insert gases and reaction gas speciesproducing selective and protective dissociated species;

C: Set of combinations of inert gases and reaction gas species producingselective dissociated species and a small quantity of non-selectivedissociated species;

D: Set of combinations of inert gases and reaction gas species producingselective dissociated species and a large quantity of non-selectivedissociated species; and

E: Set of reaction gas species dissociated by a plasma.

The combinations of reaction gases and inert gases used in the presentinvention include elements of Set A and their combinations, combinationsof elements including elements of Set A of the union of Sets A and B,combinations of elements including elements of Set A of the union ofSets A, B, and C, combinations of elements including elements of Set Ain the union of Sets A, B, and D, combinations of elements includingelements of Set A in the union of Sets A, B, C, and D, and combinationsof elements including element of Set A in the union of Sets of A, B, C,D, and E.

The following is the brief description of advantages obtained fromtypical inventions among the inventions disclosed in this application.

According to the present invention the composition of dissociatedspecies of a reaction gas can be accurately controlled and etching witha high accuracy and a high selection ratio realized. Therefore,semiconductor integrated circuit arrangements of fine structure and highintegration level can be fabricated.

What is claimed is:
 1. An integrated circuit device fabrication method,comprising the following steps;(a) forming a silicon nitride film over amajor surface of a wafer; which major surface has a gate structureincluding a gate electrode and a gate protecting insulation coveringside and upper surfaces of the gate electrode, and an isolation regionincluding a recess region and an isolating insulation therein; (b)forming a silicon oxide film over the silicon nitride film; (c) forminga patterned masking film over the silicon oxide film; (d) forming a holein the silicon oxide film by dry-etching the silicon oxide film usingthe nitride film as an etching stopper with a cyclic perfluorocarbon gaswith three or more carbon atoms under the condition that the patternedmasking film exists over the silicon oxide film and an inert gascomponent occupies no less than 50% of a first gas ambiance around thewafer, thereby exposing the silicon nitride film at the bottom of thehole; and then (e) removing the silicon nitride film at the bottom ofthe hole by etching the silicon nitride film, thereby exposing the majorsurface of the wafer at the bottom of the hole between the gatestructure and the isolation region.
 2. An integrated circuit devicefabrication method according to claim 1, wherein the inert gas componentthat occupies no less than 50% of the first gas ambiance around thewafer is an argon gas.
 3. An integrated circuit device fabricationmethod according to claim 1, wherein the inert gas component occupies noless than 80% of the first gas ambiance around the wafer, and whereinthe inert gas component is an argon gas.
 4. An integrated circuit devicefabrication method according to claim 3, wherein the cyclicperfluorocarbon gas includes C₄ F₈.
 5. An integrated circuit devicefabrication method according to claim 3, wherein the removal of thesilicon nitride film at the bottom of the hole is performed by adry-etching.
 6. An integrated circuit device fabrication methodaccording to claim 3, wherein the removal of the silicon nitride film atthe bottom of the hole is performed by a dry-etching with a non-cyclicfluorocarbon gas, under the condition that the proportion of an inertgas component occupies no less than 80% of a second gas ambiance aroundthe wafer.
 7. An integrated circuit device fabrication method accordingto claim 6, wherein the inert gas component that occupies no less than80% of the second gas ambiance around the wafer is an argon gas.
 8. Anintegrated circuit device fabrication method according to claim 7,wherein the non-cyclic fluorocarbon gas includes a carbon gas with onecarbon atom.
 9. An integrated circuit device fabrication methodaccording to claim 8, wherein the non-cyclic fluorocarbon gas is CH₂ F₂.